1. Field of the Invention
The present invention relates to a method of evaluating quality of a crystal unit, and more specifically, to a novel method capable of an accurate quality evaluation of a crystal unit.
2. Description of the Related Art
Conventionally, for quality evaluation of a crystal unit, there is used a method using a network analyzer (hereinafter referred to as a network analyzer method). In this network analyzer method, a crystal unit is considered as a passive element constituted of inductance L, capacitance C, resistance R, and a serial resonance frequency and a serial resonance resistance CI (crystal impedance) of the crystal unit is obtained by giving an AC signal thereto, and then the quality of the crystal unit is evaluated from the resultant magnitude of the CI.
However, in the network analyzer method, parameters such as CI are measured under a condition in which the crystal unit is oscillated in a stable state by the externally given signal without evaluating any transient state at the start of the oscillation in an actual oscillator. This causes a problem that a crystal unit evaluated as having good quality by the network analyzer method does not oscillate often in an actual oscillator in which the oscillation is not always in a stable state.
In view of the foregoing, it is an object of the present invention to provide a novel method of evaluating quality of a crystal unit, capable of performing quantitative measurement of an actual operation of a crystal unit which is to be oscillated in an actual oscillator to ensure an accurate quality evaluation of the crystal unit.
Here, xe2x80x9cthe quality evaluation of crystal unitxe2x80x9d means to evaluate whether the crystal unit has good or poor quality, in other words, whether the crystal unit is acceptable or unacceptable for practical use. xe2x80x9cThe crystal unit has good quality (or is acceptable)xe2x80x9d means that in an actual oscillator, an oscillation starts normally and its frequency variation is little. Hereinafter, this crystal unit is referred to simply as xe2x80x9can acceptable crystal unitxe2x80x9d. xe2x80x9cThe crystal unit has poor quality (or is unacceptable)xe2x80x9d means that in an actual oscillator, an oscillation does not start at all, or the value of CI or frequency variation is abnormally large due to variation in driving power. Hereinafter, this crystal unit is referred to simply as xe2x80x9can unacceptable crystal unitxe2x80x9d.